1. Field of the Invention
The present invention relates to a variable optical attenuator for use in optical fiber communication and optical network, and particularly to a variable optical attenuator with a stopper mechanism. A cross reference is shown in the copending application have the same title, the same inventor and the same assignee filed on Aug. 27, 2001 with an unknown serial number.
2. Description of Related Art
An optic attenuator is a passive optical component for reducing optical power propagating in a fiber, and may perform fixed or variable attenuation of optical signal. Optical attenuators are widely used in optical transmission and optical networks.
A general variable optical attenuator comprises a filter. The filter has an effective filter region located in an optical path between a collimator and a reflector. The filter has a filter density which increases from a low density region to a high density region. An optical signal can be attenuated to different extents by transmitting through different region of the filter.
For example, U.S. Pat. No. 4,702,549 describes a variable optical attenuator comprising two optical fibers having ends aligned to each other and a filter element mounted on a reciprocating means for selectively positioning the filter element between the fiber ends. The filter is not perpendicular to the axis of alignment of the fiber ends. The variable attenuator has a manual screw rod to control the attenuation of the transmitted light. A problem with the conventional attenuator is that no stopper is incorporated in the attenuator. Therefore, when the carrier with the optical filter moves between the highest attenuation position and the lowest attenuation position, the user will not know when the filter reaches the highest attenuation position or the lowest attenuation position. As a result, the user will probably over-rotate the screw rod so that the carrier moves beyond either of its extreme points. Therefore, more time will be required to readjust the filter into a desired position. More importantly, the carrier-screw rod interface will wear out more quickly since the carrier will be actuated to repeatedly move beyond the highest attenuation position or the lowest attenuation position. This will affect movement precision of the carrier on the reciprocating means. Devices of U.S. Pat. Nos. 4,989,938 and 4,904,044 share the same problem.
U.S. Pat. Nos. 6,144,794 and 6,130,984 each describe a variable optical attenuator using reciprocating means to adjust the position of the filter. Both devices employ an electrical control system. Although the electrical control systems operate with higher precision, their cost is high and they greatly increase the size of the devices.
The present invention provides a variable optical attenuator comprising a stopper structure for preventing a reciprocating movement means from over movement beyond the highest and lowest attenuation positions.
An object of the present invention is to provide an improved variable optical attenuator having a stopper mechanism for preventing the filter from moving beyond end-point positions.
Another object of the present invention is to provide an improved variable optical attenuator which can be conveniently adjusted in a relatively small and effective range.
Another object of the present invention is to provide an improved variable optical attenuator in which a carrier-screw rod interface is protected from wearing too quickly to ensure precise movement of the carrier.
A variable optical attenuator of the present invention comprises a housing to which a cover is attached for defining an interior space forming an inner cavity in a lower portion of the housing. A pair of locating slots is defined in opposite lateral sides of the inner cavity. An inner sidewall forms a forward boundary of the inner cavity. A side hole communicates between one of the locating slots and an outside wall of the housing. A fixing groove and a supporting portion are formed adjacent the other locating slot.
An optical module is accommodated in the interior space and comprises a frame, a reflector and a collimator. The frame has a groove with an inner wall, and a through hole communicating with the groove. The reflector is fixed on the inner wall of the frame and is disposed coaxially with the through hole. The collimator is positioned in the through hole and fixes ends of an input optical fiber for carrying the transmission optical signals to the attenuator and an output optical fiber for receiving the resulting attenuated transmission optical signals from the attenuator.
The reciprocating means is accommodated in the inner cavity and comprises a carrier for carrying a filter, a stopper mechanism, a stability mechanism, and a screw rod. The stopper mechanism comprises two stopper blocks and a stopper body. The stability mechanism has a fixing portion for being fixed to the carrier and a mating portion for contacting the housing. The screw rod has a threaded portion at its middle and a holding portion at each end.
When assembled, the carrier moves lengthwise along the screw rod when the screw rod is rotated. The filter that is fixed to the carrier moves along with the carrier. The stopper mechanism is formed around three sidewalls of the carrier. The stability mechanism is mounted on the carrier. The fixing portion of the stability mechanism is inserted into a fixing groove of the carrier. The mating portion of the stability mechanism abuts against the inner sidewall and moves along the inner sidewall when the carrier is moved.
By rotating the screw rod first in one direction and then in the reverse direction, the carrier with the filter can be made to move first toward one side and then toward another side of the housing. The direction of movement of the filter is perpendicular to the path of the input and output light. The filter has a filter density which varies between a low density region and a high density region along a filter axis. When the carrier arrives at one end of the screw rod, the stopper abuts with surfaces of the corresponding locating slot and the part of the filter penetrated by the input and output light will be either the low density region or the high density region. During rotation of the screw rod, the stability mechanism prevents the carrier from rotating with the screw rod and provides for stable movement of the filter, thereby ensuring precision adjustment of attenuation of optical signals.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein.